The present invention relates to thermoplastic compositions and related methods that are useful for extrusion; for example, thermoplastic extrudate compositions and extrusion coatings on various substrates, such as wood, medium density fiberboard (MDF), and synthetic substrates, articles comprising a substrate coated with the thermoplastic compositions and processes for making the articles. The compositions exhibit significant and enhanced resistance to stress, such as resistance to cracking due to extremes of heat and cold or that cracking caused by swelling due to absorption of water by the substrate or drying out of the substrate. Additionally, the compositions possess excellent mechanical properties for fabrication (cutting, nailing, routing, etc.), while maintaining acceptable visual appearance, including gloss, and surface appearance.
Manufacturers of thermoplastic compositions, such as composite compositions for horizontal blinds, indoor shutter parts, window framing, rails, doors, door frames, molding, trim and the like, have long struggled to develop compositions that exhibit enhanced mechanical properties for fabrication (hardness, toughness, lack of brittleness, scratch resistance, ability to be cut, nailed, routed, etc. without deformation or loss of structural strength), while maintaining acceptable visual appearance, including opacity, gloss, and an attractive surface appearance. By toughness is meant “a physical parameter balancing ductility and strength.” Such compositions may be comprised in, for example stress-resistant components capable of coating a variety of substrates. Other exemplary uses of such stress-resistant compositions include as a sole or primary component of a thermoplastic extrudate.
One of the most common coatings for MDF interior molding and trim available in the North American market is known as a Gesso coating. Gesso, typically used by suppliers from South America or Asia, is a thick paste that is applied using a wipe-on/wipe-off type process. Drying after coating is required, and a second coating is often applied to provide the surface with a desired look; the second coating must also be dried and buffed. Thus, Gesso coating is relatively labor intensive. Furthermore, although the Gesso coating can yield a smooth, attractive finished surface that is able to hide at least minor imperfections in the surface of the underlying substrate, it can be brittle. Brittleness of the coating may lead to unacceptable handling and fabrication performance such as cracking and splintering, for example, when the molding or trim is sawed, mitered, coped, nailed, and/or routed, or when subject to environmental conditions such as high moisture, heat and cold.
Recently attempts have been made to make thermoplastic coating components that provide good handling ability, and cosmetic appearance, particularly with attention to the ability of the coating component to accept water-based paint. Thus, U.S. patent application Ser. Nos. 12/503,675, 13/616,681, and 13/616,672 all disclose polymer coating components; these compositions are primarily suggested for enhanced paintability, including paintability using water-based paints, and comprise at least about 40% of a thermoplastic component and optional gloss, and/or opacity components; articles coated with such compositions, including painted coated articles, are also described. However, such articles still exhibit unacceptable cracking and splintering when subjected to the extremes of heat, cold, and water that would be expected, for example, upon prolonged exposure to the exterior environment.
U.S. Pat. No. 5,728,772 to Hori describes a moldable thermoplastic elastomer composition comprising a specific thermoplastic polyester elastomer alloy having comprising a copolymer having hard segments “soft segments” and a chlorinated polyethylene composition having a heat of fusion from 5 to 35 cal/g and elongation to break moduli of 670% and greater, for interior surface materials for automobiles and buildings, boots, cable coatings and other parts which are required to have rubber elasticity and heat resistance, such as packings.
U.S. Patent Publication 2004/0097650 (Ogawa) discloses a soft olefin-based moldable thermoplastic elastomer composition and having an elongation to break modulus of greater than 1000% for interior parts for automobiles.
U.S. Patent Publication 2010/0233146 (McDaniels) discloses a coating, an elastomer, an adhesive, a sealant, a textile finish, a wax, and a filler for such a material, wherein the material includes an enzyme such as an esterase.
U.S. Pat. No. 6,300,418 (to Brzoskowski) discloses an adhesive thermoplastic elastomer composition comprising either a blend of a thermoplastic resin and a rubber, or a thermoplastic elastomeric styrene-based block copolymer having elongation to break values of over 500%.
Accordingly, there remains a need in the art for compositions exhibiting improved resistance to stress—UV—or heat related cracking and fracturing under environmental conditions. Such compositions include coating components that, when applied to an underlying substrate, such as, for example, molding or trim, using extrusion technology, can result in a enhanced toughness and ductility and which also have acceptable visual appearance and scratch resistance. Preferably, such compositions also can be produced in such a way that they have a smooth finish and to have improved ability to be primed and painted, with water-based or oil-based paints.